Method for treatment of underground reservoirs

Abstract

A method for treating an underground reservoir, which method comprises introducing into the reservoir a treatment fluid comprising, dissolved or dispersed in water, an ester and a polymer breaker, such that the ester hydrolyses to produce an organic acid to dissolve acid soluble material present within the reservoir and the polymer breaker degrades polymeric material present within the reservoir.

What is claimed is:  
     
       1. A method for treating an underground reservoir, which method comprises introducing into the reservoir a treatment fluid comprising, dissolved or dispersed in water, an ester and a polymer breaker selected from the group consisting of oxidants and enzyme breakers, such that the ester hydrolyses to produce an organic acid to dissolve acid soluble material present in or adjacent to filter cake or other damage in the reservoir and the polymer breaker degrades polymeric material present in filter cake or biofilm within the reservoir. 
     
     
       2. A method according to  claim 1  wherein the underground reservoir is a hydrocarbon reservoir. 
     
     
       3. A method according to  claim 2  which further comprises recovering a hydrocarbon from the treated reservoir. 
     
     
       4. A method according to  claim 2  wherein the hydrocarbon is oil. 
     
     
       5. A method according to  claim 2  wherein the hydrocarbon is a gas. 
     
     
       6. A method according to  claim 1  wherein the underground reservoir is a water reservoir. 
     
     
       7. A method according to  claim 6  which further comprises recovering water from the treated reservoir. 
     
     
       8. A method according to  claim 1  wherein the ester is a carboxylic acid ester. 
     
     
       9. A method according to  claim 1  wherein the ester is an ester of an aliphatic carboxylic acid of formula RCO 2 H wherein R is selected from the group consisting of hydrogen, an alkyl group having from 1 to 6 carbon atoms and —R═—CO 2 H where R═ is a bond or an alkylene group having from 1 to 6 carbon atoms, the alkyl or alkylene group being unsubstituted or substituted by halogen or hydroxy. 
     
     
       10. A method according to  claim 1  wherein the ester is 1,2,3-propanetriol triacetate, 1,2,3-propanetriol diacetate, ethylene glycol diacetate, diethylene glycol diacetate or triethylene glycol diacetate. 
     
     
       11. A method according to  claim 1  wherein the ester concentration is at least about 5% w/v in the treatment fluid. 
     
     
       12. A method according to  claim 1  wherein the polymer breaker is a hydrolase enzyme. 
     
     
       13. A method according to  claim 12  wherein the enzyme is a lipase, esterase or protease enzyme. 
     
     
       14. A method according to  claim 12  wherein the or each enzyme is in the form of a delayed release preparation. 
     
     
       15. A method according to  claim 1  wherein the polymer breaker is a polysaccharide hydrolysing enzyme. 
     
     
       16. A method according to  claim 1  wherein the polymer breaker is an enzyme which can hydrolyse starch, xanthan, cellulose, guar, scleroglucan or succinoglycan or a derivative of any one of these polymers. 
     
     
       17. A method according to  claim 1  wherein the polymer breaker is an oxidant selected from the group consisting of persulphate, hypochlorite, peroxide, perborate, percarbonate, perphosphate, persilicate and a metal cation or hydrogen peroxide adduct. 
     
     
       18. A method according to  claim 1  wherein the polymer breaker is an oxidant in the form of a delayed release preparation. 
     
     
       19. A method according to  claim 1  wherein the treatment fluid further comprises an enzyme which can hydrolyse the ester. 
     
     
       20. A method according to  claim 1  wherein the treatment fluid further comprises a peroxide. 
     
     
       21. A method according to  claim 20  wherein the peroxide is a perborate or percarbonate. 
     
     
       22. A method according to  claim 1  wherein the temperature of the formation bearing the acid soluble material and polymeric material is at least 40° C. or higher. 
     
     
       23. A method according to  claim 1  wherein the treatment fluid is left in the reservoir for at least 1 hour. 
     
     
       24. A method according to  claim 1  wherein the treatment fluid is introduced into the reservoir via a wellbore which extends to the reservoir. 
     
     
       25. A method according to  claim 24  wherein the wellbore is vertical, deviated, inclined or horizontal. 
     
     
       26. A method according to  claim 1  wherein the treatment fluid is introduced into the reservoir via the drillstring. 
     
     
       27. A method according to  claim 1  wherein the treatment fluid is introduced into the reservoir via coiled tubing. 
     
     
       28. A method according to  claim 1  wherein the treatment fluid is introduced into the reservoir via bullheading. 
     
     
       29. A method according to  claim 1  wherein the treatment fluid is injected at a rate below the reservoir fracture pressure. 
     
     
       30. A method according to  claim 1  wherein the treatment fluid is injected at a rate above the reservoir fracture pressure. 
     
     
       31. A method according to  claim 1  wherein the reservoir is or includes a carbonate rock structure. 
     
     
       32. A method according to  claim 1  wherein the object of the treatment is the removal of a filter cake. 
     
     
       33. A method according to  claim 1  wherein the object of the treatment is the removal of a biofilm.